Thorpe-Ingold effect

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The Thorpe-Ingold effect or gem-dimethyl effect, or angle compression is an effect observed in organic chemistry where increasing the size of two substituents on a tetrahedral center leads to enhanced reactions between parts of the other two substituents. The effect was first reported by Beesley, Thorpe and Ingold in 1916 as part of a study of cyclization reactions.

A common application of this effect is addition of a quaternary carbon (e.g., a gem-dimethyl group) in an alkyl chain to increase the reaction rate and/or equilibrium constant of cyclization reactions. An example is this is an olefin metathesis reaction:[1]


One proposed explanation for this effect is that the increased size of the substituents increases the angle between them. As a result, the angle between the other two substituents decreases. By moving them closer together, reactions between them are accelerated.



  1. Fürstner, A. "A Concise Total Synthesis of Dactylol via Ring Closing Metathesis". J. Org. Chem. 61 (25): 8746–8749. doi:10.1021/jo961600c. Unknown parameter |coauthors= ignored (help)